The typical conventional shift scheduling system for an automatic transmission calculates the shift points and gear ratio that the transmission should be operated based upon the throttle opening of the engine and the output speed of the transmission. However, the vehicle loads, external resistances, driver's intentions (such as quick acceleration or moderate acceleration) and driving environment, etc., should also be taken into consideration to calculate the shift point and proper gear ratios in order to achieve desired vehicle performance.
In the case of transmissions which are used on vehicles having a wide variety of weights and with engines having a wide variety of governed speeds, it is important that the transmission control be sufficiently flexible to operate efficiently in each application with only minor programming changes to accommodate its environment. Another desirable aspect of flexibility is the ability to vary the shift schedule by driver control to obtain a desired economy or performance mode.
To more fully address the many influences on the vehicle performance, it is proposed to use a shift scheduling system based on the theory of fuzzy logic. In general, it is already known to use fuzzy logic techniques for transmission control. For example, U.S. Pat. No. 4,841,815 to Takahashi issued Jun. 17, 1989, uses a number of inputs, such as vehicle speed, engine load, running resistance and gear position to determine the degrees of fuzziness or the adequacy of the current gear position, the upshift gear position and the downshift gear position, thereby determining whether a shift is desirable.
It is preferable in certain applications, however, to base an evaluation of relative performance on the turbine speed of the transmission in order to determine the optimum shift point to maintain the turbine speed in the proper range, as defined by the engine governed speed, without regard for the current gear position. This allows the transmission to be used with engines of widely different governed speeds without special calibration other than inputting the governed speed. Decisions about lockup clutch control, on the other hand, may profitably take into account the gear position as well as a shift parameter determined through fuzzy logic.